Well drilling and completion fluid composition

ABSTRACT

An improved well drilling and completion fluid composition which has excellent stability over a broad temperature range, has a low tubular goods corrosion rate, prevents the sloughing of clay-containing materials and is environmentally acceptable. The composition is comprised of water, a viscosity increasing agent, a fluid loss reducer and rheology stabilizer and one or more water-soluble clay-stabilizing organic salts.

A great variety of aqueous drilling and completion fluid compositionshave been developed and used heretofore. Problems which have beencommonly encountered in the use of such drilling and completion fluidsare that when high temperatures are encountered, the fluids becomeunstable, i.e., the viscosity and other properties are lost or reduced,and when the fluids come into contact with water-sensitiveclay-containing formations or strata, the clay-containing materialsslough off the walls of the well bore into the fluids. The sloughing offormation materials into the drilling and completion fluids causesvarious problems including the contamination of the fluids and the lossof desired fluid properties.

Heretofore, the sloughing of clay-containing formation materials, e.g.,water-sensitive shales, penetrated by well bores when contacted byaqueous drilling or completion fluids has been reduced by includingpotassium chloride or potassium hydroxide in the drilling or completionfluids. While aqueous fluids containing potassium chloride or potassiumhydroxide are effective in reducing the swelling of clays and thesloughing of clay-containing materials when in contact therewith, anumber of other problems are inherent in the use of such solutions.

Drilling fluids containing potassium chloride in the quantity requiredto provide sufficient potassium ion concentration to prevent clayswelling and sloughing of formation materials frequently havedemonstrated unstable rheological and filtration control properties. Thehigh chloride ion content also causes the fluids to be more corrosive totubular goods in the well bore and creates disposal problems. Inaddition, high chloride ion levels in drilling and completion fluidsmake electric logs and other analytical procedures carried out thereinmore difficult to interpret.

The use of potassium hydroxide in lieu of potassium chloride bringsabout more stable drilling and completion fluids, but the quantity ofpotassium hydroxide that can be used must be limited to prevent thefluids from becoming excessively caustic and corrosive. The presence ofhydroxyl ions in the fluids offsets the effectiveness of potassium ionstherein because hydroxyl ions promote hydration of clays. Further,dispersants must normally be used in drilling or completion fluidscontaining potassium hydroxide which bring about the adverse result ofdispersing cuttings in the fluids.

Other potassium compounds such as potassium carbonate and potassiumbicarbonate have been utilized in well treatment fluids, but suchcompounds also cause the fluids to be unstable, etc.

By the present invention, an improved drilling and completion fluid isprovided which can be weighted with solid weighting agents to obtaindensities from about 8.5 to about 19 pounds per gallon, which has a hightolerance for solids and cement contamination, which is insensitive tosalt water intrusion, which can be used at temperatures up to 450° F.without losing desired rheological properties, which has a low tubulargoods corrosion rate, which prevents or reduces the sloughing ofwater-soluble clay-containing materials when in contact therewith andwhich is environmentally acceptable allowing the fluid to be readilydisposed of without elaborate procedures being carried out forprotecting the environment.

The drilling and completion fluid compositions of this invention arecomprised of water, a viscosity increasing agent which also functions asa fluid loss reducer, a fluid loss reducing and rheology stabilizingagent and a clay-stabilizing agent, i.e., an agent which substantiallyprevents the sloughing of water-sensitive clay-containing materialscontacted by the compositions, but which does not make the compositionshighly corrosive or toxic. The compositions can optionally include solidweighting agents, additional rheology stabilizers and basic compoundsfor adjusting the pH of the composition to desired levels.

The water utilized in the compositions can be fresh water, brines orseawater and the viscosity increasing agent can be any of a variety ofhydratable gelling agents which hydrate in the water used to increasethe viscosity thereof. Examples of such viscosity increasing agents arexanthum gum, hydroxyethylcellulose, sepiolite clay, attapulgite, andmontmorillonite clay. Of the foregoing, sepiolite clay and attapulgiteclay are preferred in that they readily increase the viscosity of freshwater, brines and salt water and do not lose stability at hightemperatures, i.e., such viscosity increasing agents are stable andmaintain the viscosity of an aqueous composition over a temperaturerange up to about 450° F. The most preferred viscosity increasing agentfor use in the compositions of this invention is sepiolite clay.

The fluid loss reducing and rheology stabilizing agent utilized inaccordance with the present invention is selected from the groupconsisting of pregelatinized starch, vinylamide-vinylsulfonateterpolymer, hydroxyethylcellulose and mixtures thereof. If the drillingand completion fluid composition is to be subjected to temperaturesbelow about 250° F., pregelatinized starch is preferred for itsrelatively low cost. When the composition is to be subjected totemperatures in the range of from about 250° F. up to about 450° F.,vinylamide-vinylsulfonate terpolymer is preferred in that it retains itsstability and effectiveness at such temperatures. As indicated, thefluid loss reducing and rheology stabilizing agent reduces fluid loss topermeable formations encountered in a well bore and functions tomaintain the drilling or completion fluid rheological properties at asubstantially constant level in spite of solids and cementcontamination, salt water intrusion and high temperatures.

The vinylamide-vinylsulfonate terpolymer is available as a fine whitegranular solid and is prepared by reacting 2-acrylamido-2methyl-3-propyl sodium sulfonate, vinylacetamide and acrylamide monomersto form a terpolymer thereof. The terpolymer is readily dissolvable infresh water, salt water and seawater, and as mentioned above, theterpolymer remains stable and effective over broad pH and temperatureranges. The terpolymer and its synthesis are described in greater detailin West German Patent No. 2,931,897 dated Feb. 26, 1981, which isincorporated herein by reference and which corresponds to U.S. Pat. No.4,309,523, issued Jan. 5, 1982.

The clay-stabilizing agent functions to prevent the hydration andswelling of clays and the resultant sloughing of clay-containingmaterials when in contact with the compositions. The clay-stabilizingagent utilized in accordance with the present invention is awater-soluble clay-stabilizing organic acid salt or mixture of saltshaving the general formula: ##STR1## wherein: R is hydrogen or a methyl,ethyl or propyl radical; and M is potassium, rubidium, cesium orammonium.

Such organic acid salts are readily soluble in water, brines andseawater and the cations thereof, i.e., potassium, rubidium, cesium andammonium, react with or otherwise prevent water-sensitive clays fromswelling and migrating. The anionic portions of the compounds arenon-reactive with clays, are non-toxic and do not form insolublecompounds with cations normally present in subterranean formations suchas sodium, calcium and magnesium. Examples of particularly suitable suchcompounds are potassium formate, potassium acetate, potassiumpropionate, potassium butyrate, rubidium formate, rubidium acetate,cesium formate, cesium acetate, ammonium formate, ammonium acetate,ammonium propionate, and ammonium butyrate.

Preferred such clay-stabilizing salts for use in accordance with thepresent invention are compounds as defined above wherein M is potassium.Of these, potassium acetate is the most preferred.

As mentioned above, the compositions preferably also include a base,such as sodium or potassium hydroxide present therein in a quantitysufficient to adjust the pH of the composition to a level in the rangeof from about 8.5 to about 11.5. At such pH range, the compositions arestable and relatively non-corrosive to metal tubular goods.

In addition, the compositions can optionally include a solid weightingagent, such as barite, hematite, etc., for increasing the densitythereof to desired levels. The weighting agent can be present in thecompositions in an amount such that the compositions have a density ashigh as 19 pounds per gallon while remaining stable, etc. When aweighting agent is included in the compositions it is also advantageousto include an additional rheology stabilizer therein which facilitatesthe dispersal and suspension of the weighting agent in the compositions.Particularly suitable such rheology stabilizers are the sodium salt ofpolymerized alkyl naphthalene sulfonic acid (polymerized alkylnaphthalene sodium sulfonate), citric acid and gluconic acid.

A particularly suitable drilling and completion fluid of the presentinvention is comprised of water, a viscosity increasing agent selectedfrom the group consisting of sepiolite clay, and attapulgite claypresent in the composition in an amount in the range of from about 1 toabout 50 pounds per barrel of fluid, a fluid loss reducing and rheologystabilizing agent selected from the group consisting of pregelatinizedstarch, vinylamide-vinylsulfonate terpolymer and mixtures thereofpresent in the composition in an amount in the range of from about 1 toabout 30 pounds per barrel of fluid, and a clay stabilizing agentcomprised of a water-soluble organic acid salt selected from the groupconsisting of a salt or mixture of salts having the general formula:##STR2## wherein: R is hydrogen or a methyl, ethyl or propyl radical,and M is potassium, rubidium, cesium or ammonium, the clay stabilizingagent being present in the composition in an amount in the range of fromabout 1 to about 100 pounds per barrel of fluid.

The above composition can include one or more weighting agents such asbarite, hematite, etc., in an amount sufficient to increase the densitythereof up to about 19 pounds per gallon, i.e., an amount in the rangeof from about 5 to about 600 pounds per barrel of fluid. As mentionedabove, the composition can also include sodium or potassium hydroxide inan amount to adjust the pH to a level in the range of from about 8.5 toabout 12.0, i.e., a quantity in the range of from about 0 to about 5pounds per barrel of fluid and an additional rheology stabilizer, e.g.,polymerized alkyl naphthalene sodium sulfonate, in a quantity in therange of from about 0 to about 5 pounds per barrel of fluid.

A preferred well drilling and completion fluid composition of thisinvention is comprised of water, sepiolite clay viscosity increasingagent present in the composition an amount in the range of from about 10to about 30 pounds per barrel of composition, a fluid loss reducer andrheology stabilizer selected from the group consisting of pregelatinizedstarch, vinylamide-vinylsulfonate terpolymer and mixtures thereofpresent in said composition in an amount in the range of from about 1 toabout 20 pounds per barrel of composition, a clay stabilizing agentcomprised of a water-soluble organic acid salt selected from the groupconsisting of a salt or mixture of salts having the general formula:##STR3## wherein: R is hydrogen or a methyl, ethyl or propyl radical,and M is potassium, the clay stabilizing agent being present in thecomposition in an amount in the range of from about 1 to about 30 poundsper barrel of composition, and sodium hydroxide present in thecomposition in an amount sufficient to adjust the pH thereof to a levelin the range of from about 8 to about 11.5.

Another preferred weighted composition is as defined above and includingbarite solid weighting agent present in the composition in an amount inthe range of from about 5 to about 600 pounds per barrel and a rheologystabilizing agent comprised of the sodium salt of polymerized alkylnaphthalene sulfonic acid present in the composition in an amount in therange of from about 1/4 to about 10 pounds per barrel of composition.

The most preferred composition of the present invention is comprised ofwater, sepiolite clay viscosity increasing agent present in thecomposition in an amount of about 10-25 pounds per barrel ofcomposition, vinylamide-vinylsulfonate terpolymer fluid loss reducingand rheology stabilizing agent present in the composition in an amountof about 3-5 pounds per barrel of composition, potassium acetate claystabilizing agent present in the composition in the amount of about 10pounds per barrel of composition, sodium hydroxide present in thecomposition in an amount sufficient to adjust the pH of the compositionto 9.5, barite weighting agent present in the composition in an amountsufficient to increase the density thereof to a density in the range offrom about 8.5 to about 19 pounds per gallon and a rheology stabilizingagent comprised of the sodium salt of polymerized alkyl naphthalenesulfonic acid present in the composition in an amount of about 0.5 poundper barrel of composition.

In order to facilitate a clear understanding of the compositions of thepresent invention, the following examples are given.

EXAMPLE 1

Drilling or completion fluid formulations are prepared as follows. Addpotassium acetate to seawater and mix to dissolve (about 2 minutes). Addsepiolite clay and mix for 8 minutes to allow the sepiolite to hydrate.Add vinylamide-vinylsulfonate terpolymer, followed by the sodium salt ofpolymerized alkyl naphthalene sulfonic acid. Adjust the pH of thesolution with caustic soda to around 9.0. For a weighted system, add thenecessary quantity of barite and mix for another 10 minutes.

The properties of weighted and unweighted fluid formulations prepared inaccordance with the above procedure are given in Table I below.

                                      TABLE I                                     __________________________________________________________________________    FLUID FORMULATION PROPERTIES                                                  Sample No.                                                                             1      2      3      4      5                                        Conditions                                                                             I   HR I   HR I   HR I   HR I   HR                                   __________________________________________________________________________    Water, ml.                                                                             350    332    300    279    252                                      Sea salt, ppb                                                                          14.7   14.0   12.6   11.0   10.6                                     Potassium                                                                              10.0   9.5    8.6    8.0    7.2                                      acetate, ppb                                                                  Sepiolite, ppb                                                                         25.0   22.5   20.0   15.0   12.5                                     Terpolymer, ppb                                                                        3.0    3.0    3.0    3.0    3.0                                      Sodium hydroxide,                                                                      0.25   0.25   0.25   0.25   0.25                                     ppb                                                                           Alkyl naphthalene                                                             Sodium sulfonate,                                                                      0.5    0.5    0.5    0.5    0.5                                      ppb                                                                           Barite, ppb     78     203    299    410                                      YP, #/100 ft.sup.2                                                                     2   3  6   4  2   4  4   2  2   10                                   Gels, I/10                                                                             2/2 2/2                                                                              2/4 2/3                                                                              2/3 1/3                                                                              2/4 2/5                                                                              4/8 4/8                                  minutes                                                                       pH       9.5 9.0                                                                              9.5 9.0                                                                              9.5 8.9                                                                              9.5 8.8                                                                              9.6 8.8                                  API fluid loss,                                                                            10.6                 8.8                                         ml.                                                                           Weight, ppg                                                                            8.6    10.0   12.0   14.0   16.0                                     mg/1 K   10,000*       10,175*       10,450*                                  __________________________________________________________________________     I = initial                                                                   HR = hot rolled 16 hours at 150° F.                                    *Analysis by atomic absorption                                           

EXAMPLE 2

The fluid formulations shown in Table I and prepared in accordance withthe procedure given in Example 1 are tested for tolerance to solidscontamination. Grundite shale is used as the solid contaminant. Theshale has the following composition:

    ______________________________________                                        quartz.           20-22%                                                      Pyrite            3-5%                                                        Chlorite          4-6%                                                        Illite            40-45%                                                      Smectite and mixed                                                                              21-25%                                                      layer clays                                                                   Amorphous         4-6%                                                        CEC* = 10.6 meq/100 grams shale                                               Potassium            248    mg/l                                              Magnesium            1250   mg/l                                              Calcium              2710   mg/l                                              Sodium               42     mg/l                                              ______________________________________                                    

The results of the solids contamination tests are summarized in Table IIbelow.

                  TABLE II                                                        ______________________________________                                        DRILLING OR COMPLETION FLUID FORMULATION                                      TOLERANCE TO DRILL SOLIDS                                                     Percent Solids                                                                          Fluid Weight,                                                                            YP        Gels                                           (ppb solids)                                                                            ppg        I      HR   I     HR                                     ______________________________________                                         0 (0)    8.6        2      3    2/2   2/2                                     3 (10.5) 8.6        2      0    1/2   1/1                                     6 (21.0) 8.6        2      1    1/1   1/3                                    10 (35.0) 8.6        2      1    0/2   1/2                                    15 (52.5) 8.6        2      4    2/4   1/3                                     0 (0)    10.0       6      4    2/4   2/3                                     3 (10.5) 10.0       8      4    3/4   2/3                                     6 (21.0) 10.0       4      6    2/4   3/3                                    10 (35.0) 10.0       6      6    2/4   2/3                                    15 (52.5) 10.0       6      4    2/6   2/5                                     0 (0)    12.0       2      4    2/3   1/3                                     3 (10.5) 12.0       0      4    2/3   1/4                                     6 (21.0) 12.0       2      4    2/3   1/3                                    10 (35.0) 12.0       4      4    2/4   2/3                                    15 (52.5) 12.0       4      4    2/5   2/6                                     0 (0)    14.0       4      2    2/4   2/5                                     3 (10.5) 14.0       0      2    2/3   3/5                                     6 (21.0) 14.0       3      4    3/5   2/5                                    10 (35.0) 14.0       4      4    2/5   2/6                                    15 (52.5) 14.0       6      4    2/6   2/7                                    20 (70.0) 14.0       10     12    3/13  4/12                                  25 (87.5) 14.0       16     16    4/20  5/19                                  30 (105)  14.0       22     26    5/28  8/29                                  ______________________________________                                    

Up to 70 ppb solids are tolerated by the formulations withoutsignificant changes in the rheology even at 14 ppg mud weight. Solids upto 105 ppb added to a 14 ppg fluid increase the yield point and thegels, although the rheological properties are still acceptable. Theterpolymer is kept at 3 ppb in all the tests. Increasing theconcentration of the vinylamide-vinylsulfonate terpolymer promotesrheological stabilization and higher levels of solids can be toleratedby the fluid formulations.

EXAMPLE 3

Drilling or completion fluids of various weights are formulated inaccordance with the procedure of Example 1 and the quantities ofcomponents given in Table I, except the concentration of the alkylnaphthalene sodium sulfonate is increased to 5 ppb. The fluids aretested for green cement contamination by adding 3% green cement and 10%drill solids to the fluids. The results are summarized in Table IIIbelow.

                                      TABLE III                                   __________________________________________________________________________    DRILLING OR COMPLETION FLUID TOLERANCE                                        TO GREEN CEMENT CONTAMINATION                                                          Weight, ppg                                                                   8.6   10.0  12.0  14.0  16.0                                                  I  HR I  HR I  HR I  HR I  HR                                        __________________________________________________________________________    PV, cps  8  10 12 12 19 22 24 25 36 50                                        YP, lbs/100 ft.sup.2                                                                   2  2  2  4  4  10 2  8  12 22                                        Gels,    2/3                                                                              1/3                                                                              2/2                                                                              2/5                                                                              2/4                                                                              4/17                                                                             2/4                                                                              4/13                                                                             4/22                                                                             17/52                                     pH       11.3                                                                             11.9                                                                             11.3                                                                             11.8                                                                             11.4                                                                             11.8                                                                             11.4                                                                             11.8                                                                             11.5                                                                             11.8                                      API fluid loss,cc                                                                         19.0  17.5  13.5  12.2                                            __________________________________________________________________________     I = initial                                                                   HR = hotrolled 16 hours at 150° F.                                

Rheological properties can be improved by the addition of more alkylnaphthalene sodium sulfonate or the vinylamide-vinylsulfonateterpolymer. The latter is more effective. For example, the addition of 2ppb of the alkyl naphthalene sodium sulfonate to a 16 ppg sample,hot-rolled for 16 hours, decreases the yield point from 22 to 16 andgels from 17/52 to 5/25. On the other hand, the addition of 2 ppb of theterpolymer brings the yield point from 22 to 4 and the gels from 17/52to 2/3.

EXAMPLE 4

The procedure of Example 3 is repeated except that 5% green cement and10% drill solids are used. The 5% green cement and 10% drill solidsresult in higher but still acceptable gels. The fluid formulations areas shown in Table I except the alkyl naphthalene sodium sulfonate levelis raised to 6 ppb. The results of these tests are given in Table IVbelow.

                                      TABLE IV                                    __________________________________________________________________________    DRILLING OR COMPLETION FLUID TOLERANCE                                        TO GREEN CEMENT CONTAMINATION                                                         Weight, ppg                                                                   8.6    10.0  12.0   14.0  16.0                                                I  HR  I  HR I  HR  I  HR I  HR                                       __________________________________________________________________________    PV, cps 12 11  12 17 19 24  23 26 32 40                                       YP, lbs/100 ft.sup.2                                                                  0  24  2  11 4  20  2  12 10 28                                       Gels,   2/3                                                                              23/47                                                                             2/3                                                                              5/28                                                                             2/11                                                                             14/51                                                                             2/13                                                                             5/35                                                                             5/32                                                                             15/76                                    pH      11.8                                                                             12.0                                                                              11.8                                                                             12.0                                                                             11.8                                                                             12.0                                                                              11.8                                                                             12.0                                                                             11.7                                                                             11.8                                     __________________________________________________________________________     I = initial                                                                   HR = hotrolled 16 hours at 150° F.                                

EXAMPLE 5

The temperature stability of water-based drilling or completion fluidsis often limited by the polymeric components. The terpolymer used inthis system is stable to over 450° F. and is resistant to hydrolysis.

The temperature stability of the 14 ppg fluid shown in Table I ismodified to include 5 ppb vinylamide/vinylsulfonate polymer and 1 ppbalkyl naphthalene sodium sulfonate.

    ______________________________________                                        Fluid Properties:                                                             ______________________________________                                        PV, cps          31                                                           YP, lbs/100 ft.sup.2                                                                           8                                                            Gels             3/4                                                          API fluid loss, cc                                                                             6.6                                                          HTHP filtrate    34.0                                                         (300° F.), cc                                                          pH               9.5                                                          ______________________________________                                    

The effect of temperature and pressure on the fluid is determined usinga Model 50 Fann consistometer. The fluid becomes thin with highertemperature and pressure and recovers its consistency on cooling asshown in Table V below.

                  TABLE V                                                         ______________________________________                                        CONSISTOMETER DATA                                                            Temperature,   Pressure,                                                                              Consistometer                                         °F.     psi      Units*                                                ______________________________________                                         75            1,000    56                                                    100            2,000    44                                                    150            4,000    36                                                    200            7,000    30                                                    250            8,000    26                                                    300            9,000    24                                                    350            9,500    20                                                    375            9,500    20                                                    400            10,000   22                                                    440            10,000   12                                                    cooled to 75            50                                                    ______________________________________                                         *arbitrary units?                                                        

The rheological properties of the 14 ppg fluid, contaminated with 35 ppbdrill solids, remains stable after 16 hours static aging at 350° F. asshown in Table VI below.

                  TABLE VI                                                        ______________________________________                                        EFFECT OF TEMPERATURE ON RHEOLOGY                                             Drilling or Completion Fluid:                                                                         14    ppg                                             Drill Solids:           35    ppb                                             Terpolymer:             5     ppb                                             Properties       Initial Static-Aged                                          ______________________________________                                        PV, cps          32      21                                                   YP, lbs/100 ft.sup.2                                                                           8       6                                                    Gels             2/4     2/5                                                  pH               7.1     7.1                                                  API filtrate, cc         14.5                                                 ______________________________________                                    

EXAMPLE 6

Shale stabilization tests are conducted with gumbo shale (containingover 50% smectite) to determine how much potassium is needed for optimumstabilization. Small pieces of gumbo shale are added to unweightedfluids with varying amounts of potassium and hot-rolled for 16 hours at150° F. The results of these tests are given in Table VII below.

                  TABLE VII                                                       ______________________________________                                        DRILLING AND COMPLETION                                                       FLUID SHALE STABILIZATION                                                     ppb CH.sub.3 CO.sub.2 K                                                                  5      10     15    20   25   30                                   ______________________________________                                        ppm K*     5650          16250           32250                                Wt. of shale,                                                                            21.43  14.67  11.48 12.51                                                                              10.32                                                                              9.46                                 init., grams                                                                  Wt. of shale,                                                                            18.17  11.08   9.64 10.02                                                                               8.22                                                                              7.92                                 after hot-                                                                    rolling                                                                       Wt. loss, grams                                                                           3.26   3.59   1.84  2.49                                                                               2.10                                                                              1.54                                 % loss     15.21  24.47  16.03 19.90                                                                              20.45                                                                              16.28                                ______________________________________                                         *analysis by atomic absorption                                           

Each shale sample remains in solid form with no cracks. Each sampleshows signs of dehydration. The results indicate that even with 5 ppb(less than 1% K), fluids have good clay stabilization properties.

EXAMPLE 7

The fluids of this invention can be prepared in fresh water. Otherpolymers, such as starch, hydroxyethylcellulose, etc., can besubstituted for the terpolymer in low temperature applications. Thestarch-containing fluids can be converted to high temperature fluids ifneeded. Examples of fresh water formulations with different polymers aregiven in Tables VIII and IX below.

                                      TABLE VIII                                  __________________________________________________________________________    FRESH WATER, UNWEIGHTED FLUIDS                                                __________________________________________________________________________                 1      2      3      4                                           __________________________________________________________________________    Additives, ppb                                                                Potassium acetate                                                                          10.0   10.0   10.0   10.0                                        Sepiolite    15.0   15.0   15.0   15.0                                        Starch       10.0   5.0    7.0    10.0                                        Vinylamide-vinylsulfonate  2.0                                                terpolymer                                                                    Alkyl naphthalene sodium                                                                   0.5    0.5    0.5                                                sulfonate                                                                     Hydroxyethylcellulose                                                                             2.0                                                       Sodium hydroxide                                                                           0.25   0.25   0.25   0.25                                        __________________________________________________________________________                 I   HR I   HR I   HR I   HR                                      __________________________________________________________________________    AV, cps      13  12 8   6.5                                                                              9   9  8   10                                      PV, cps      8   7  8   6  8   8  6   7                                       YP, lbs/100 ft.sup.2                                                                       10  10 0   1  2   2  4   6                                       Gels         4/7 4/7                                                                              0/2 0/2                                                                              0/2 1/2                                                                              2/8 2/8                                     pH           10.8                                                                              9.8                                                                              10.7                                                                              9.8                                                                              10.1                                                                              9.7                                                                              10.5                                                                              10.6                                    API fluid loss, cc                                                                             6.0    10.6   6.5    6.0                                     ppm Potassium                                                                              10,000 10,000 10,000 10,000                                      __________________________________________________________________________     I = initial                                                                   HR = hotrolled for 16 hours at 150° F.                            

                                      TABLE IX                                    __________________________________________________________________________    FRESH WATER, WEIGHTED FLUIDS                                                  __________________________________________________________________________                 1      2       3      4                                          __________________________________________________________________________    Additives, ppb                                                                Potassium acetate                                                                          9.5    8.6     8.0    6.5                                        Sepiolite    15.0   15.0    15.0   10.0                                       Starch       10.0   10.0    10.0                                              Vinylamide-vinylsulfonate          3.0                                        terpolymer                                                                    Alkyl naphthalene sodium                                                                   0.5    0.5     5.0    5.0                                        sulfonate                                                                     Sodium hydroxide                                                                           0.25   0.25    0.25   0.5                                        Barite       78.0   203.0   299.0  564.0                                      __________________________________________________________________________                 I   HR I   HR  I   HR I   HR                                     __________________________________________________________________________    AV, cps      12  13 23  28  32.5                                                                              34 71  66                                     PV, cps      9   8  16  12  20  25 50  48                                     YP, lbs/100 ft.sup.2                                                                       6   10 14  32  25  18 42  35                                     Gels         0/4 2/17                                                                             4/29                                                                              24/50                                                                             8/14                                                                              9/30                                                                             10/46                                                                             7/25                                   pH               9.9    9.3     8.5    8.2                                    API fluid loss, cc                                                                             5.8    9.6     7.0K   5.6                                    Wt. ppg      10.0   12.0    14.0   18.6                                       ppm Potassium                                                                              10,000 10,000  10,000 10,000                                     __________________________________________________________________________     I = initial                                                                   HR = hotrolled for 16 hours at 150° F.                            

EXAMPLE 8

The fresh water fluids are also tested for tolerance to solidscontamination. The results are summarized in Table X below. Formulation1, with no potassium acetate, gives high yield point and gels. In thepresence of potassium acetate (Formulation 2), the yield points and thegels are much lower. This demonstrates that potassium acetate hasexcellent inhibition on the clays (sepiolite and grundite). Formulation3 with 70 ppb drill solids shows insignificant changes in rheologicalproperties. The addition of the terpolymer causes further lowering ofthe yield point and the gels.

                                      TABLE X                                     __________________________________________________________________________    TOLERANCE TO SOLIDS CONTAMINATION, FRESH WATER FLUIDS                         __________________________________________________________________________                 1       2      3      4                                          __________________________________________________________________________    Additives, ppb                                                                Potassium acetate    10.0   10.0   10.0                                       Sepiolite    15.0    15.0   15.0   15.0                                       Starch                             7.0                                        Vinylamide-vinylsulfonate          2.0                                        terpolymer                                                                    Alkyl naphthalene sodium                                                                   0.5     0.5    0.5    0.5                                        sulfonate                                                                     Sodium hydroxide                                                                           0.25    0.25   0.25   0.25                                       Grundite Shale                                                                             35.0    35.0   70.0   70.0                                       __________________________________________________________________________                 I   HR  I   HR I   HR I   HR                                     __________________________________________________________________________    AV, cps      67  53  13  12 14  13 13  12                                     PV, cps      28  14  10  9  10  10 12  11                                     YP, lbs/100 ft..sup.2                                                                      78  78  6   6  7   5  2   2                                      Gels         16/22                                                                             38/38                                                                             3/6 3/8                                                                              3/10                                                                              3/7                                                                              2/2 2/2                                    ppm Potassium                                                                              0.0     10,000 10,000 10,000                                     __________________________________________________________________________     I = initial                                                                   HR = hotrolled for 16 hours at 150° F.                            

EXAMPLE 9

Fresh Water fluids are prepared containing 10,000 ppm K using potassiumchloride and potassium acetate. Pieces of gumbo shale with over 50%smectite are immersed in the fluids and hot-rolled for 16 hours at 150°F. The potassium acetate demonstrates better shale stabilizationqualities.

    ______________________________________                                        Data:                                                                         ______________________________________                                        (1)     KCl fluid                                                                     Wt. of gumbo shale    7.45 grams                                              After 16 hrs., 150° F. hot-rolling                                                           6.00 grams                                              Weight loss           1.45 grams                                              % weight loss        19.45%                                           (2)     CH.sub.3 CO.sub.2 K fluid                                                     Weight of gumbo shale                                                                               7.45 grams                                              After 16 hrs., 150° F. hot-rolling                                                           6.48 grams                                              Weight loss           0.97 grams                                              % weight loss        13.02%                                           ______________________________________                                    

EXAMPLE 10

Corrosion is a problem with potassium chloride solutions which are muchbelow saturation levels. The potassium acetate fluid is tested forcorrosion properties.

Solutions of potassium chloride and potassium acetate are preparedcontaining 10,000 ppm K. Corrosion tests are run for 167 hours at 150°F. With the KCl fluid, the corrosion rate is 13 mils per year while withthe potassium acetate fluid, the corrosion rate is 3.6 mils per year, afourfold improvement.

EXAMPLE 11

Aqueous solutions (fresh water) of potassium acetate, potassium formate,ammonium formate, ammonium acetate and rubidium acetate are preparedcontaining 10,000 ppm of cation. Pieces of gumbo shale with over 50%smectite are immersed in the solutions and hot-rolled for 16 hours at150° F. For comparison purposes pieces of the same gumbo shale arehot-rolled for the same time and temperature in fresh water alone and ina fresh water solution of potassium citrate. The results of these testsare given in Table III below.

                  TABLE XI                                                        ______________________________________                                        SHALE STABILIZATION BY VARIOUS                                                ORGANIC ACID SALTS                                                                    Initial  Weight of                                                            Gumbo    Gumbo Shale                                                  Organic Shale    After Hot   Weight     pH                                    Acid Salt                                                                             Weight,  Rolling,    Loss, %    of                                    Used    gms.     gms.        gms.  Loss Solution                              ______________________________________                                        None    8.83     0 (Shale    8.83  100  7.2                                                    Disintegrated)                                               Potassium                                                                             5.42     4.47        0.95  17.53                                                                              8.4                                   Acetate                                                                       Potassium                                                                             7.55     6.80        0.75  9.93 7.8                                   Formate                                                                       Ammonium                                                                              8.79     8.40        0.39  4.44 7.8                                   Formate                                                                       Ammonium                                                                              7.62     7.45        0.17  2.23 7.9                                   Acetate                                                                       Rubidium                                                                              4.39     4.17        0.22  5.01 8.0                                   Acetate                                                                       Potassium                                                                             8.39     5.43        2.96  35.28                                                                              9.5                                   Citrate                                                                       ______________________________________                                    

From Table III it can be seen that the various organic acid saltsutilized in accordance with the present invention provide excellentshale stabilization.

We claim:
 1. A well drilling and completion fluid composition consistingessentially of:water; sepiolite clay viscosity increasing agent presentin said composition in an amount in the range of from about 1 to about50 pounds per barrel of composition; vinylamide-vinylsulfonateterpolymer fluid loss reducing and rheology stabilizing agent present insaid composition in an amount in the range of from about 1 to about 30pounds per barrel of composition, said terpolymer being prepared by thereaction of 2-acrylamide-2 methyl-3-propyl sodium sulfonate,vinylacetamide and acrylamide monomers; sodium hydroxide present in saidcomposition in an amount in the range of from about 1/8 to about 2pounds per barrel of composition; and potassium acetate clay stabilizingagent present in said composition in an amount in the range of fromabout 1 to about 100 pounds per barrel of composition.
 2. Thecomposition of claim 1 which is further characterized to include a solidweighting agent present in said composition in a quantity sufficient toincrease the density thereof to a level in the range of from about 8.5to about 19 pounds per gallon of composition.